In clinical and preclinical research studies, data from various modalities are used to aid investigation regarding a drug or treatment. Data from multiple modalities (such as CT, MR, PET or SPECT) yield different information, and a combination of such information may be used in order to arrive at a conclusion. For example, PET and SPECT data may yield functional information, whereas CT and MR may yield anatomical information. In order to fuse such information, the anatomical region to be studied (such as an organ or a tumor region) may be first delineated in the CT or MR image. The functional ability of the same region is then studied via information from PET or SPECT images. In order to ensure that the same region is studied in both the modalities, an initial registration between the images may be carried out of the data to ensure that the size, overlap and orientation of the two images are comparable. In addition, registration may also be performed to compensate for differences in acquisition conditions, biological variability, and motion. However, the assessment of functional ability allows for improvement.